1. Field of the Invention
This invention relates to chain saws having automatic lubricating systems wherein the lubrication is pumped to the saw chain and guide bar in reaction to engagement of the clutch for driving the saw chain, and more particularly it relates to a member that combines the functions of generating the drive for the lubricating pump and providing a seal around the pump to protect against dust and dirt contamination.
2. Background Information
On motorized chain saws, an endless saw chain is propelled by a drive sprocket coupled to a centrifugal clutch and is guided and travels in a formed groove in an elongated guide bar. The saw chain is guided and travels in the groove of the guide bar in a sliding metal-to-metal contact. To prevent heat build up, which could damage both the saw chain and guide bar, caused by the sliding metal-to-metal contact and also to reduce friction, a lubricating system is incorporated within the chain saw housing.
The lubricating system has a reservoir that provides a supply of oil to a pump mechanism. When driven, the pump mechanism delivers oil to an aperture in the side wall of the groove of the guide bar via a connecting passageway, thereby providing lubricant to the saw chain and the groove of the guide bar.
The lubricating systems on most chain saws are automatic. That is, oil is supplied to the saw chain and guide bar only when the saw chain is propelled by the engagement of the centrifugal clutch. To provide this automatic feature, the pump drive is therefore also coupled to the centrifugal clutch that propels the saw chain.
In a common embodiment, the lubricating pump drive is coupled to the centrifugal clutch by utilizing a worm gear drive in the form of a threaded hub that is in turn driven by the shaft of the driven clutch cup. (This shaft is commonly referred to as the adapter in that it adapts a particular drive sprocket to the standard chain saw drive.) The worm gear driver is in mesh with a worm gear, and when rotated by the clutch cup, it in turn provides rotation to the worm gear which drives the pump mechanism.
Since chain saws are operated in an environment where wood chips, sawdust and other debris are always present, a seal is provided to protect the pump drive components from these elements. The seal is typically a plastic cylindrical disc that is mounted and rotates with the adapter of the clutch cup. It has a protruding lip on its periphery. A metal washer is sometimes used between the seal and the face of the housing. The face of the housing has a circular groove or recess and the lip of the seal is designed to rotate inside the groove of the housing to cooperatively seal out the debris.
The mounting of the seal in the above-described fashion has some shortcomings. The adapter and the clutch cup to which it is rigidly attached, by design, is permitted some axial float on the drive shaft of the chain saw. The seal being attached to the adapter will float or move away from the housing when the adapter and hub move axially away from the housing face. Movement of the seal away from the housing face provides a space for the entrance of wood chips, dust, etc. into the pump drive mechanism. The seal could also become partially dislodged from its frictional mount and therefore would wobble during rotation and provide an opening for entrance of wood chips, etc.